Steering the Dynamics of Reaction Intermediates and Catalyst Surface during Electrochemical Pulsed CO 2 Reduction for Enhanced C 2+ Selectivity.

Developing alternative electrolysis techniques is crucial for advancing electrocatalysis in addition to tremendous efforts of material developments. Recently, pulse electrochemical CO 2 reduction reaction (CO 2 RR) has demonstrated dramatic selectivity improvement toward multicarbon (C 2+ ) products compared to potentiostatic electrochemical CO 2 RR, yet the underlying mechanisms remain little understood. Herein, we develop a fast time-resolved in situ Raman spectroscopic method with a time resolution of 0.25 s. We reveal that pulse electrolysis improves the C 2+ selectivity of CO 2 RR through dynamic controls of the surface Cu x O/Cu composition that would be unachievable under potentiostatic electrolysis. The population of the surface-adsorbed CO intermediate (CO ads ) is characterized to be the determining factor in controlling reaction selectivity, which depicts the C 2+ /C 1 selectivity of CO 2 RR under pulse conditions. Meanwhile, the vibrational character of CO ads , despite transforming dynamically between the low-frequency and high-frequency modes is characterized not to be the key factor in controlling the reaction selectivity. Such an active control of catalyst surface compositions and reaction intermediates enabled by pulse electrolysis offer a general way of regulating the electrocatalysis performance of broad electrochemical reactions beyond CO 2 RR.